Modified start sequence of a gas turbine engine

Abstract

A system for controlling a start sequence of a gas turbine engine includes an electronic engine control system, a thermal model, memory, a model for determining a time period (tmotoring), and a controller. The thermal model synthesizes a heat state of the gas turbine engine. The memory records the current heat state at shutdown and a shutdown time of the gas turbine engine. The model for determining the time period is for motoring the gas turbine engine at a predetermined speed Ntarget that is less than a speed to start the gas turbine engine, where tmotoring is a function of the heat state recorded at engine shutdown and an elapsed time of an engine start request relative to a previous shutdown time. The controller modulates a starter valve to maintain the gas turbine engine within a predetermined speed range of NtargetMin to NtargetMax for homogenizing engine temperatures.

What is claimed is: 
     
       1. A gas turbine engine and a system for controlling a start sequence of the gas turbine engine, comprising:
 an electronic engine control system; 
 a thermal model resident upon the electronic engine control system and configured to synthesize a heat state of the gas turbine engine; 
 a memory for recording a current heat state of the gas turbine engine at shutdown and for recording a shutdown time of the gas turbine engine; 
 a model for determining a time period for motoring the gas turbine engine at a predetermined speed wherein the predetermined speed is less than a speed used to start the gas turbine engine and wherein the time period is a function of the heat state recorded at engine shutdown and an elapsed time of an engine start request relative to a previous shutdown time; and 
 a controller for modulating a starter valve of a starter of the gas turbine engine in order to maintain the gas turbine engine within a predetermined speed range for homogenizing engine temperatures. 
 
     
     
       2. The gas turbine engine and system of  claim 1 , wherein the time period is calculated automatically during a start of the gas turbine engine. 
     
     
       3. The gas turbine engine and system of  claim 1 , wherein the controller modulates a duty cycle of the starter valve via pulse width modulation. 
     
     
       4. The gas turbine engine and system of  claim 1 , wherein the starter valve controls a flow of an air supply into the starter of the gas turbine engine. 
     
     
       5. A method for providing a start sequence of a gas turbine engine, comprising:
 determining a heat state of the gas turbine engine via an engine thermal model; 
 storing the heat state of the gas turbine engine at engine shutdown; 
 recording a time of the engine shutdown; and 
 using a risk model to determine a motoring time period for a start sequence of the gas turbine engine, wherein the risk model uses the recorded time of the engine shutdown and the stored heat state of the gas turbine engine at the engine shut-down to determine the motoring time period. 
 
     
     
       6. The method as in  claim 5 , wherein the gas turbine engine is motored at a predetermined speed range the motoring time period, which is less than a normal idle start speed. 
     
     
       7. The method as in  claim 6 , further comprising dynamically varying a position of a starter valve during the motoring time period in order to motor the gas turbine engine at the predetermined speed range. 
     
     
       8. The method as in  claim 5 , wherein the risk model is located on an electronic control of a system programmed to automatically implement the motoring time period. 
     
     
       9. The method as in  claim 8 , wherein the heat state is determined by a first thermal model and a second thermal model each being resident upon the electronic control. 
     
     
       10. The method as in  claim 5 , further comprising providing a time of an engine start request and an inlet air temperature to the risk model when the risk model determines the motoring time period. 
     
     
       11. The method as in  claim 5 , wherein the motoring time period determines a duration of a modified start sequence of the gas turbine engine and the modified start sequence requires motoring of the gas turbine engine at a predetermined speed during the motoring time period without introduction of fuel and an ignition source to the gas turbine engine, wherein the predetermined speed is less than a normal idle start speed.